1. Field of the Invention
The invention relates generally to the field of networking. More particularly, it relates to the field of home networking, as employed in coupling electronic devices to each other, such as via home telephone lines.
2. Background
Home Networking is a new segment of the networking marketplace that is poised for rapid growth. Achieving the goals needed to make home networking a market success is a challenging task, however. The nascent home networking market growth will depend on the emergence of high-speed broadband access as a catalyst as well as on the availability of robust, low cost, easy to install standardized home networking equipment. Technical analysis has demonstrated that there is little system margin available for achieving the desired rates and robustness if a trouble-free consumer experience is desired. To enrich the consumer experience it is critical to consider mechanisms in the system that can be employed to support simple to use remote diagnostic tools in these emerging systems.
Home networking utilizes the telephone wiring within a household as a communication cable for use by networked devices within the home (e.g., a computer to a printer). However, the same inside telephone wiring may simultaneously carry several categories and/or types of signals, analog and/or digital in a frequency division multiplexed (FDM) topology. For instance, a single telephone line may be used to carry plain old telephone service (POTS), ISDN, and/or xDSL services such as ADSL and/or VDSL.
FIG. 4 shows a spectrum utilization of POTS, HPN, and various xDSL services arranged in a frequency division multiplexed topology.
In particular, as shown in FIG. 4, Plain Old Telephone Service (POTS) exists in the 0-4 kHz region, xDSL service is present from 25 kHz to approximately 2.2 MHz (depending on the definition of xe2x80x9cxxe2x80x9d), and the Home Networking spectrum occupies 5.5-9.5 MHz for HPN V1.x technology and 4.75-9.25 MHz for the emerging HPN V2 technology. The spectral allocation for the VDSL services is not yet established but it is expected to use the 26 kHz to 12 MHz region. The HPN signals occupy a spectrum which is higher in frequency than POTS, ISDN, ADSL and VDSL.
Although HPN communications are not intended for locations outside the customer""s premises, some level of the HPN signal may be present on the subscriber loop pair (i.e., telephone line) that services the premise""s telephone wiring. Normally this does not cause a problem to the telephone company because the HPN signal is almost always attenuated below the ambient noise floor before reaching the central office (CO) end of the subscriber loop.
FIG. 5 shows the source and existence of cross talk between an HPN signal and a VDSL signal in a common binder.
In particular, as shown in FIG. 5, where the subscriber loop pair is combined with other pairs into a cable, the potential exists for crosstalk into an adjacent pair. For instance, where adjacent pairs in a binder group carry VDSL services, and the downstream VDSL signal overlaps the HPN band, an HPN signal may appear as crosstalk in the receiver of the VDSL modem.
Since the frequency plan for VDSL is not yet established, it is difficult to definitively estimate the impact of HPN on VDSL. The severity and frequency of occurrence of such potential crosstalk is highly dependent on many variables, not yet accurately captured in deployment models. While further study may be required in this area, analysis performed to date indicates that the probability of interference into the VDSL service by HPN terminals does exist at least in some instances.
It is widely believed that the primary technical solution to VDSL-HPN crosstalk is the installation of a Network Isolation Filter (NIF) between the premises wiring and the outside subscriber loop. Such a filter blocks transmission of signals at 4 MHz and higher, but would pass signals under 4 MHz (providing for POTS, ISDN and ADSL).
FIG. 6 shows the use of a network isolation filter (NIF) on a subscriber loop (i.e., telephone line) installed at the customer""s premises.
One of the difficulties faced by service providers before they can install a network isolation filter or other device to correct a problem is in identifying the source of a problem in response to a customer""s complaint, e.g., a complaint that a subscriber""s VDSL services are not operating correctly. As a result, numerous test and fault isolation systems have been developed for testing the operability of various components in the telephone network to determine if the problem resides in the customer premise equipment (CPE), in the line drop connecting the CPE to the switching system, or elsewhere in the telephone network system. These test and fault isolation systems are readily available to telecommunication service providers.
For instance, in one test technique described by the Home Phoneline Networking Alliance (xe2x80x9cHPNxe2x80x9d) 1.0 and 2.0 specifications, a PSD mask that extends from 4 to 10 MHz is used. HPN signals are imposed by the test equipment on the existing telephone wiring inside a dwelling or office, and are used for local communication between HPN stations.
It is important to consider that the emerging xe2x80x9cin-homexe2x80x9d networking technology is being targeted as a consumer grade service. As such, any design goals must consider the xe2x80x9ctechnology challengedxe2x80x9d consumer and require xe2x80x9cout of the boxxe2x80x9d functionality. In the case of xe2x80x9cin-homexe2x80x9d networking via existing telephone cable (HPN), the expectation from the consumer simply is that the technology will function properly and require little more than installing a telephone cable into an available telephone jack in the home. Furthermore, it is typically expected that the technology will provide a path to install upper level protocols and drivers with no network configuration, required by the consumer. This model obviously assumes that no xe2x80x9ctruck rollxe2x80x9d occurs requiring an in-home service call by a qualified service technician.
HPN devices can be used without prior installation of a NIF. HPN technology has been designed to be robust in the face of noise coupled into the premises wiring from the subscriber loop, such as Amateur Radio Service RFI, crosstalk from adjacent loops with other HPN devices, and even crosstalk from VDSL. HPN operation is optimized, however, with the provisioning of a NIF. However, the average consumer can not be expected to install the NIF within the residence.
There are likely to be several situations that will result in NIFs being successfully introduced:
1) Installation on the subscriber""s line of broadband access services such as ADSL or VDSL that employ a splitter (which also functions as a NIF).
2) Provisioning with alternate POTS services that derive a local POTS interface for the premises wiring from a broadband gateway or network termination unit.
3) Telephone operating company installation of an NIF to remediate VDSL interference as part of ongoing loop-plant maintenance procedures. This may be accomplished with an xe2x80x9cadd-onxe2x80x9d NIF filter, or via upgrade of the subscriber""s NID with one that has been designed with an integrated HPN NIF.
In any event, it is preferred that the consumer need not install an NIF filter themselves. To this end, there is a need for apparatus and techniques which allow a telephone company to detect, isolate, and correct effects of home networking on the telephone system.
In accordance with the principles of the present invention, a home network telephone line signature circuit comprises a voltage breakdown element having a breakdown in excess of 80 volts. An impedance is placed in series with the voltage breakdown element. The voltage breakdown element and the impedance are adapted for placement in series across a telephone line supporting a home network.
A method of indicating a presence of a home network device on a telephone line in accordance with another aspect of the present invention comprises sensing a voltage level of an injected energy signal on the telephone line. If the sensed voltage level exceeds at least 80 volts, a shunt impedance is activated across the telephone line.